The present invention relates to adjustable rearview mirror support structures, and more particularly relates to mirror support structures that provide full angular adjustment while still meeting anti-vibration functional requirements and position-to-driver distance requirements.
Vibration is a problem with many vehicle rearview mirror systems, because the mirror heads are typically supported in cantilever off of a vehicle component, such as off of a front windshield or overhead console. The problem is related to vibrational amplitude and vibrational frequency of the mirror head, as it relates to the driver's eyes. The problem is compounded when the front windshield is used for support, because the glass of the windshield can flex, bend and move, in addition to gross vehicle movement from bumps and road-and-travel-caused vibrations. In particular, mirror mounts attached farther from a top edge of the front windshield glass have a greater tendency to vibrate, because the glass tends to bend and flex a greater amount at locations spaced away from the top glass edge where stiff vehicle frame members support the glass and prevent bending and flexing. Further, the longer the length of the cantilever arm (i.e., the greater the distance from the windshield to the mirror head), the greater the tendency to have greater vibration and/or to have vibratory mechanical resonance that causes greater amplitudes. Also, ball-and-socket pivot joints can aggravate the problem.
The vibration problem can be reduced by positioning a mirror head closer to a front windshield or by mounting it higher on the windshield. However, this may not be acceptable for several reasons. Vehicle manufacturers have numerous requirements concerning the position and angular adjustability of the mirror head relative to the vehicle driver. For example, the mirror head must be low enough so that the driver has a good rearward field of view. The mirror head must be physically close enough to the driver so that the driver can reach any buttons on the mirror head, and also can easily reach the mirror head for making an angular adjustment. The mirror head must have a defined range of angular adjustability, so that all drivers can adequately adjust the mirror head for their individual preference. However, with large front windshields, particularly where the front windshield extends relatively high, or where the windshield has a low near-horizontal angle, it is extremely difficult to meet all three requirements of 1) driver-reachable button locations on the mirror, 2) sufficiently high enough near-the-top-edge mount location on the windshield to minimize vibration problems (while still being low enough to minimize the cantilever arm length), and 3) providing the required range of angular adjustment for the mirror to meet the requirements of different body sizes and preferences of drivers.
In addition there is another subtle problem. Most modern mirror support structures incorporate a ball-and-socket joint that is angularly adjustable. A torsional strength of the ball-and-socket joints is increased as the ball section diameter is increased. This is because the torque that holds a selected adjusted position is related to the friction forces times the radius of the ball section (i.e., the torque arm of the frictional force is equal to a radius of the ball section). However, as the radius of the ball section is increased, so does a weight of the mounting structure, which can in turn lead to increased vibration problems. Also, the size of the overall support structure increases as components are made larger, which reduces visibility out the front windshield by the vehicle driver. Accordingly, there is tension between the requirement for a stability (i.e., a larger radius on the ball section) and the requirement for low weight and size (i.e., a smaller radius of the ball section).
FIG. 1 illustrates a typical two-ball-and-socket mirror support arrangement, where a mirror head 20 is supported by a two-ball-and-socket mount 21 on a vehicle front windshield 22. The details of the mount 21 are eliminated in FIG. 1 to better show the dimensional and motion considerations of interior rearview mirrors; but one example of a mount 21 is illustrated in FIG. 1A. The mount 21 includes a mirror-attached mount component 23, a tubular connector 24, and a window-attached second mount component 25 defining first and second ball-and-socket connections 26 and 27 (each made up of a ball section and a socket). In FIG. 1, the ball-and-socket connections 26 and 27 are not shown, but their location is shown by center points 28 and 29. As illustrated in FIG. 1A, the mirror head 20 has a center of gravity 30 located about a distance 31 from the center point 28 of the first ball section. This results in a vibrational effect shown by arrows 32. The tubular connector 24 has a length with ends extending slightly longer than the distance 33 between the center points 28 and 29, which results is a second vibrational effect shown by arrows 34. The window-attached mount component 25 defines a length 35 between the windshield 22 and the ball section 29, which results in a third vibrational effect shown by arrows 37. The windshield 22 can vibrate longitudinally along its length (as shown by arrow 38, such as due to gross vehicle movement from road bumps or wheel imbalances) or it can bend with a drum-like movement (see arrows 39 and 39A). This drumming movement tends to be greater at locations spaced farther from the edge 40 of the windshield 36 since the sheet metal edge support structure 41 both stiffly supports the glass and also potentially dampens vibration. Also, the drumming movement is greatly affected by a size of the front windshield 22, and by the angle of inclination 42 of the windshield relative to horizontal.
Another important factor is the distance 43 from the mirror head to the vehicle driver. In FIG. 1A, where the windshield 36 is a considerable distance from the vehicle driver's eyes and reach, the tubular connector 24 is often elongated to make up the distance. However, this aggravates the pendulum effects illustrated by arrows 32 and 34. The problem of vibration of the mirror head 20 is also aggravated where the mirror is supported relatively lower on the windshield 22 (i.e., farther from the edge support structure 41) a distance 39B. It is important to keep in mind that, in additional to all of the above criteria, the angular adjustability of the mirror head 20 must be maintained so that individual drivers can adjust the mirror for optimal viewing and for individual preferences. In the arrangement of FIG. 1A, the mirror head 20 can only be adjusted with small upward angles 43 and 44 about ball-and-socket connections due to interference at locations 47 and 48 with ends of the outer tube section of connector 24, while the mirror head 20 can be angularly adjustable downwardly through large angles 45 and 46 about the ball-and-socket connections. This downward adjustability is largely wasted, since much of the downward adjustability is unused, while the upward adjustability is severely limited by engagement of ends of the tubular connector 24 with the material of the mount components 23 and 25.
Accordingly, a mirror support arrangement is desired solving the aforementioned problems and having the aforementioned advantages.